Idaho Power Company has operated a cloud seeding program since 2003 to enhance snowpack and increase water supply. The program uses both ground-based generators and aircraft to seed winter storms when conditions are suitable. Trace chemical analyses and snowpack density measurements provide evidence that seeding increases snowpack amounts. Cloud physics data from instrumented aircraft also indicate that seeding stimulates ice crystal formation. The program aims to flexibly target a wide area and make use of both airborne and ground-based seeding to maximize effectiveness.
2. Background
• IPC started evaluating cloud seeding based on a shareowner
inquiry in 1993
• Literature review – 1993 - 1994
• Data collection -1995 (climatology and background silver levels)
• One year program in winter 1996-97
• Operational program started in late winter 2003
• Included two year assessment
3. Presentation Overview
• What is cloud seeding?
• How we know cloud seeding works…
• IPC’s history with cloud seeding…
• IPC’s cloud seeding program…
4. What is cloud seeding?
• The term cloud seeding has been used to describe:
– Fog suppression (airports)
– Hail suppression (reduce crop and property damage)
– Rainfall enhancement (water supply augmentation)
– Snowpack enhancement (snowpack augmentation)
• Our focus is snowpack enhancement
• First, some overview of precipitation process
5. Precipitation…
• A given column of air has a limited amount of water vapor it can
hold
• For precipitation to occur, the air column must be at or near
saturation (i.e. relative humidity ≈ 100%)
• Relative humidity is a function of temperature (warm air can hold
more water vapor than cold air)
• However, saturation alone does not lead to precipitation
• Ice nuclei are required for water vapor to convert to ice crystals
• Ice nuclei are found naturally in the atmosphere, but may be
limited relative to available water vapor
• This limitation can provide an opportunity….
7. Atmospheric Water
Vapor
• There is a lot more water
vapor in the atmosphere
than we can see.
• Not all water vapor is
visible as clouds.
8. Cloud Seeding
The key is super cooled liquid water…
Water that is in a vapor state, but below freezing.
9. Cloud Seeding
• Cloud seeding provides mother nature with ice nuclei
• But, it is only effective when ice nuclei are limiting and nature is
performing the other required precipitation processes
– cloud seeding doesn’t create clouds to seed – it will not cure a drought!
• Effectiveness depends on:
– temperatures,
– available water vapor,
– ice nuclei properties,
– cloud droplet and natural ice distributions
• Several agents can be used as ice nuclei, with silver iodide (AgI)
being the most common used in commercial cloud seeding.
10. Cloud Seeding
Where did it get started?
• In 1946 at GE labs in Schenectady, NY, it was discovered that
various materials can initiate the formation and growth of water
droplets and ice crystals (leading to cloud seeding).
Building on those early discoveries,
• Cloud seeding is conducted in over 40 countries
• Numerous projects in US, including some dating to the 1950’s
12. Cloud Seeding –
Wintertime Orographic
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depoliting &Ome of the cloud water on lhe groond
13. Silver Iodide Distribution
• In commercial programs, silver iodide is burned to release silver
iodide particles (ice nuclei) of an appropriate size to the
atmosphere.
• Ground generators - Acetone – silver iodide solution is burned in a
propane flame.
• Aircraft - silver iodide is incorporated into a flare, or solution is
burned.
19. Cloud Seeding
• Lots of evidence that it works in laboratory and controlled
conditions.
• The big question – how do we know it puts snow on the ground?
• Plume tracing – UT pulsed seeding experiment
• Trace chemistry (IPC’s dual tracer)
• Aircraft data collection
23. IPC’s Dual Tracer
Assessment
Approach
• IPC needed to demonstrate that project can effectively put seeding
material in target area, and that seeding increases snowpack as
expected.
• Independent contractors performed assessment
• Co-located seeding and tracer generators
– Release seeding and tracer at same rate
• Silver iodide (AgI) released from both ground and aircraft
generators.
• Silver incorporated into snowpack through ice nucleating (seeding)
process or scavenging
• Inert tracers (non-nucleating) incorporated in snowpack through
scavenging process only.
25. Ice Nucleation vs.
Scavenging
Indium oxide nano-particles are
passively incorporated into snow
crystals (scavenged).
Silver Iodide nano-particles actively
cause ice crystal formation (seeding)
26. IPC’s Dual Tracer
Assessment
Approach (cont.)
• Following seeding, sample snowpack for evaluation of trace levels
of silver, indium, and cesium as well as snowpack density
• Ratio of silver to tracer (ex. Indium) in the snow pack gives an
indication of how much silver deposited by ice nucleating vs.
scavenging processes.
27. Snow Sampling
and Ground Generator Sites
Ground
Generators
D2
D1
Low
B1
B3
B2WH
NB
MZ
T1
T2
T3
T4
T5
OT1
SP
MC
BC
NGV
CC MM KR
BM
Control Sites
2003-2004
Sites
2004-2005
Sites
New sites were sampled in 2004 -2005 due to access problems in 2003-
2004.
28. Sampling Snow Pack
• Snow samples collected using ultra-trace ‘metal clean’
techniques and acid cleaned equipment.
29. Analytical Methods
• Samples acidified with ultra-pure
nitric acid in class 100 clean room.
• Analysis by High Resolution
Inductively Coupled Plasma Mass
Spectrometry.
• Detection limits of ~ 300 parts per
quadrillion for silver
– 300 / 1,000,000,000,000,000 (1015)
• Think of it as a single drop of water
in a sports arena like the Idaho
Center (Nampa, ID)
30. Targeting from
Chemistry Data
• Targeting of the seeding
operations was assessed by
integrating the silver found in
the snow over a given storm
period to estimate the total
amount of silver deposited
during the storm.
December 6 through 9, 2004
March 5 and 6, 2004
Control
site
MC
BC
NG
V MM
KR BM
MC
BC
NG
V MM
KR BM
CM
Ground-generator Site
= silver
deposited
100 x 10 -12 g
= silver 100 g
released
Example Targeting Maps for the March
2004 and December 2004 storm periods
31. Aircraft Targeting
• Aircraft seeding identified
by using a cesium tracer.
• Identification of aircraft
tracer was complicated by
dust – cesium, which was
also deposited in the snow .
Aircraft
Cesium
Cesium
from dust
2D profile of snow cesium
32. Targeting Results
• The amount of silver deposited downwind of active ground
generators was much greater than that found at the control sites.
• Silver deposition maps show that the center of the target area was
affected by the seeding operations.
• Indium concentrations were generally very low
– Silver not from scavenging
• Evidence for targeting by aircraft was found in the center of the
target area in December 2004.
• The project layout and operations can effectively hit the target area
with both ground generators and aircraft.
• Determining precipitation increases…
37. 2004 Cloud Physics
• Two planes – seeding and
research aircraft.
• Research aircraft fitted
with a number of probes to
measure parameters
important to precipitation
38. 2004 Cloud Physics
Cloud physics data collected just
prior to the onset of airborne
seeding. In particular, note the
second and third frames, and
compare them to the following
diagram.
Time (GMT)
07:10:00 07:20:00 07:30:00 07:40:00
Altitude(m)
1000
1500
2000
2500
3000
3500
4000
VerticalVelocity(m/s)
-500
0
500
1000
1500
Altitude (m)
Vertical Velocity
Temperature(
o
C)
-10
-5
0
5
10
Dewpoint(o
C)
-10
-5
0
5
10
Dewpoint
Temperature
FSSPLWC(gm-3)
0.0
0.5
1.0
DMTLWC(g/m
3
)
0.5
1.0
1.5
2.0
LWC
FSSP LWC
MixingRatio(g/kg)
2
4
6
8
SaturationVapor
Pressure(mb)
2
3
4
5
6
MixRatio
SatVap
MeanIce
CrystalSize(um)
100
200
300
MedianIce
CrystalSize(um)
0
100
200
300
Mean (um)
MVD (um)
2DCTotalIce
Concentration(#/l)
100
200
300
400
ShadowOrCrystal
Concentration(#/l)
0
200
400
600
800
Total Accepted Conc.
ShadowOr Conc.
39. 2004 Cloud Physics
The same data as in the previous figure, but
shortly after the initiation of airborne seeding.
Note that the total ice mass increases
dramatically about 20 minutes after the onset
of seeding while at the same time, the mean
ice crystal size decreases.
Indicative of conversion of supercooled liquid
water into new ice crystals that can then grow
into snowflakes.
Time (GMT)
08:15:00 08:25:00 08:35:00 08:45:00
Altitude(m)
3000
3200
3400
3600
3800
4000
VerticalVelocity(m/s)
-500
0
500
1000
1500Altitude (m)
Vertical Velocity
Temperature(
o
C)
-10
-5
0
5
10
Dewpoint(o
C)
-10
-5
0
5
10
Dewpoint
Temperature
08:15:00 08:25:00 08:35:00 08:45:00
FSSPLWC(gm-3)
0.0
0.5
1.0
DMTLWC(g/m
3
)
0.2
0.4
0.6
0.8
1.0
FSSP LWC
DMT LWC
MixingRatio(g/kg)
2
4
6
8
SaturationVapor
Pressure(mb)
2
3
4
5
6
MixRatio
SatVap
MeanIce
CrystalSize(um)
100
200
300
MedianIce
CrystalSize(um)
0
100
200
300
Mean (um)
MVD (um)
2DCTotalIce
Concentration(#/l)
100
200
300
400
ShadowOrCrystal
Concentration(#/l)
0
200
400
600
800
Total Accepted Conc.
ShadowOr Conc.
40. Trace Chemistry
Summary
• Due to compaction of the snow pack, water increases could not be
estimated for the 2003-2004 season.
• During 2004-2005, DRI concluded cloud seeding revealed an
average increase of 7%. Individual storm events ranged between
7 and 35% increases.
• Under favorable conditions, greater increases may be obtained
through longer seeding periods.
• Moving to flares significantly increases seeding potential from the
aircraft.
41. How do others view
cloud seeding?
• During California energy crisis while PG&E was facing
bankruptcy, the CA PUC advised PG&E that they would continue
their cloud seeding programs during reorganization.
• PG&E is working to expand their project
42. Idaho Power’s Cloud
Seeding Project
• At the request of shareholders – began investigating cloud seeding in 1993
• Literature review 1993 and 1994
• Climatology study water year 1994-95
• Contracted operational program in 1996-97
• Planned to perform internal program in 1997-98
– canceled do to no mechanism to recover project expenses and share benefits
• Reinstated in Feb 2003.
• Operational including assessment in fall of 2003
• Completed second year of assessment and third year of operations in May 2005.
• Currently in final stages of 5th operational year
43. Idaho Power’s Cloud
Seeding Project
IPC views cloud seeding as a long-term water management tool.
Project Organization
• In literature review, found expert opinions that some commercial
programs benefit public relations more than anything else.
• Most long-term programs have an in-house component -
representing stakeholders interest.
• Rather than commission entire project, IPC elected to employ key
personnel to represent the Company’s interest.
• A 3rd party provides aircraft and conducted an assessment.
44. Current Project
Organization
Internal
• Forecasting, project operations (dispatch balloon launches, ground
and aircraft seeding), equipment fabrication and maintenance,
solution mixing, data (NOAA port), communications and control
software.
• Project staff
– 2 staff meteorologists (forecasting, operations)
– 2 water resource specialists (ground gens)
– shared time - administration, data acquisition and communication
External
• Aircraft and pilots
• Weather balloon launches
• Part time forecasting meteorologist
45. Effective Program
An effective program includes:
• Knowledge of:
– Water content – is the storm conducive to seed?
– Temperature profile
– Wind speed and direction
• The wrong combination of temperature and water content can easily lead to
reduced precipitation.
• Winds effect targeting
• Flexibility – ability to seed a range of conditions
• Aircraft safety
– Flying a plane in storm conditions – pilot needs guidance regarding severe
ice, lightning, etc.
46. Both Airborne and
Ground-based
• Seeding intended to enhance
snowpack at the higher elevations
above 4500’
• Target area ~ 938 sq. miles
• ~ 497 mi2 above the 6000’ level
• Combined approach provides
more opportunities for addressing
storms.
• Complementary
Too warm for ground, can still fly,
too cold to fly, can still use the
ground units, or,
Use both at the same time
58. Benefit Summary
2008 Benefits estimate using:
• USBR regression equation for Payette at Horseshoe Bend
– Using current 2008 conditions (near normal)
• Precipitation increase of 10% from cloud seeding
• Results in approximately 100 KAF of additional Mar – Jul runoff
Estimated cost per acre-foot of additional water ≈ $8.50